drm/i915/dp: Refactor FEC support check in intel_dp_supports_dsc

Forward Error Correction is required for DP if we are using DSC but
is optional for eDP.

Currently the helper intel_dp_supports_dsc checks if fec_enable is set for
DP or not. The helper is called after fec_enable is set in crtc_state.

Instead of this a better approach would be to:
first, call intel_dp_supports_dsc to check for DSC support
(along with FEC requirement for DP) and then set fec_enable for DP
(if not already set) in crtc_state.

To achieve this, remove the check for fec_enable in the helper and instead
check for FEC support for DP. With this change the helper
intel_dp_supports_dsc can be called earlier and return early if DSC is
not supported. The structure intel_dp is added to the helper to get the
FEC support for DP.

v2: Pass intel_dp to adjust_limits_for_dsc_hblank_expansion_quirk
instead of deriving it from connector. (Jani)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217093244.3938132-2-ankit.k.nautiyal@intel.com